1. Field of the Invention
This invention relates to balanced linear motor compressors which operate without the use of oil and externally tuned resonant balancers. Such structures of this type, generally, provide a highly reliable oil-free compressor which is internally balanced for use with cryogenic refrigeration equipment so as to attain unattended, continuous operation without maintenance over extended periods of time.
2. Description of the Related Art
It is known in cryorefrigerator compressors, to employ petroleum-based oil as the lubricant. Typically, a petroleum-based oil dissolves gases such as air and hydrocarbons which come in contact with the cooling gases over time. When the oil in the compressor interacts with the cooling gases pumped by the compressor into the cold head, the oil releases the air into the cooling gases. Thus, a portion of air dissolved into the oil is carried by the cooling gases into the cold head. When the cooling gases contact the cold head, which, typically is maintained at temperatures below 77K, the air condenses and solidifies on the cold head cold surfaces. The solidification of the air can adversely affect the cold head operation because it plugs up the regenerators, reduces the piston clearances and wears out the piston seals. Ultimately, the reduced capacity of the cold head can affect the overall performance of the cryorefrigerator. Therefore, a more advantageous compressor would be presented if the oil could be eliminated.
Also, linear compressors which are not internally balanced require externally tuned resonant balancers. While these external balancers have exhibited a modicum of success in dampening out the vibration created by the linear compressors, the use of the external balancer inherently adds complexity and cost to the cryorefrigerator. Therefore, a still further advantageous compressor would be presented if the oil and the external balancers could be eliminated.
It is apparent from the above that there exists a need in the art for a compressor which is internally balanced and which, at least, equals the cooling characteristics of the known cryorefrigerator compressors, but which at the same time is oil-free so that the contamination and unreliability associated with cold heads employing oil lubricants are reduced. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.